ON AND8222-D Thermal considerations for the on semiconductor Datasheet

AND8391/D
Thermal Considerations for
the ON Semiconductor
Family of Discrete Constant
Current Regulators (CCR)
for Driving LEDs in
Automotive Applications
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APPLICATION NOTE
Prepared by: Mike Sweador (AE),
David Helzer (PE)
ON Semiconductor
Introduction
Reference to Datasheet
The ON Semiconductor Constant Current Regulator
(CCR) family of devices offer outstanding regulation for
LEDs and other current based loads, such as battery
charging circuits. The CCR reduces the complexity of
resistor biased designs for sensitive loads, such as LED
strings connected in series. The CCR can also be connected
in parallel for higher load current applications. The
two−terminal CCR requires no external components to
regulate at the specified current. These devices can be used
wherever a constant current is needed to maintain
luminosity under varying voltage conditions.
See application note AND8349/D for basic circuit
considerations.
The purpose of this paper is to explore the temperature and
power boundaries for devices in the SOD−123 and
SOT−223 packages operating from typical currents of
20 mA to 30 mA in automotive applications. The SOD−123
devices available are rated at 20 mA, 25 mA, and 30 mA.
The SOT−223 devices are rated at 25 mA and 30 mA. See
Appendix A for device list.
The datasheet describes the devices and defines the
following terms that will be used throughout this note:
Vak = Voltage applied between the Anode and Cathode of
the device.
Voverhead = VIN − VLEDs
Ireg(SS) = The current through the device supplied to the
LEDs under steady−state operating conditions (device on
w10 sec)
Ireg(P) = The current through the device supplied to the LEDs
under pulse test conditions (v 300 msec).
VR = Reverse Voltage
PD = Device power dissipation, typically in mW.
TA = Ambient Temperature in °C
TJ = Device Junction Temperature in °C
The SOD−123 and SOT−223 Datasheet Thermal
Characteristics table lists the thermal performance of each
device as related to the heat spreader area and thickness.
These datasheet tables and curves show thermal
specifications and limits with the device junction
temperature (TJ) operating at 150°C, the maximum
allowable continuous junction temperature.
Operating at TJ max continuously is not recommended for
long term reliability.
Figure 1 shows power dissipation over changes in
ambient temperature for the SOD−123 package. Figure 2
shows qJA (°C/W) and PD (W) for various Cu areas and
thicknesses. These tables and graphs illustrate the effect of
Cu area, thickness and ambient temperature (TA) over the
range of −40°C to 85°C, which encompasses the area of
interest for automotive LED operation. LED data sheets
show an extreme reduction in luminosity above 85°C TA.
© Semiconductor Components Industries, LLC, 2009
August, 2009 − Rev. 2
1
Publication Order Number:
AND8391/D
AND8391/D
700
PD max @ 855C
500 mm2 2 oz
500 mm2 1 oz
600
300 mm2 2 oz
500
300 mm2 1 oz
400
300
100 mm2 2 oz
200
100
−40
500 mm2 2 oz Cu
241 mW
500 mm2 1 oz Cu
228 mW
300 mm2 2 oz Cu
189 mW
300
mm2
1 oz Cu
182 mW
100
mm2
2 oz Cu
117 mW
100
mm2
1 oz Cu
108 mW
100 mm2 1 oz
−20
0
20
40
60
80
TA, AMBIENT TEMPERATURE (°C)
Figure 1. Power Dissipation vs. Ambient
Temperature (SOD−123) @ TJ = 1505C for Variable
Copper Heat Spreader
1200
0.6
TA = 25°C
0.5
1000
Power Curve 2.0 oz Cu
qJA, (°C/W)
800
0.4
Power Curve 1.0 oz Cu
600
0.3
400
qJA 1.0 oz Cu
0.2
200
qJA 2.0 oz Cu
0.1
0
0
100
200
300
400
500
600
0
700
PCB COPPER AREA (mm2)
Figure 2. SOD−123 NSI14030T1G qJA and PD vs. Cu Area
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2
MAXIMUM POWER (W)
PD, POWER DISSIPATION (mW)
800
AND8391/D
NOTE: 300 mm2 2 oz Cu area has better thermal
performance than 500 mm2 1 oz Cu for this package.
Figure 3 shows power dissipation over changes in
ambient temperature for the SOT−223 package. Figure 4
shows qJA (°C/W) and PD (W) for various Cu areas and
thicknesses. These tables and graphs illustrate the effect of
Cu area, thickness and ambient temperature (TA ) over the
range of −40°C to 85°C which encompasses the area of
interest for automotive LED operation.
2200
PD, POWER DISSIPATION (mW)
PD max @ 855C
500 mm2 2 oz
2000
500 mm2 2 oz Cu
300 mm2 2 oz
1800
500 mm2 1 oz
1600
300 mm2 1 oz
1400
1200
100 mm2 1 oz
1000
722 mW
300
mm2
2 oz Cu
676 mW
500
mm2
1 oz Cu
631 mW
300
mm2
1 oz Cu
598 mW
100
mm2
2 oz Cu
559 mW
100 mm2 1 oz Cu
494 mW
800
600
100 mm2 2 oz
400
−40
−20
0
20
40
60
TA, AMBIENT TEMPERATURE (°C)
80
Figure 3. Power Dissipation vs. Ambient
Temperature (SOT−223) @ TJ = 1505C
180
1.5
Power Curve 2.0 oz Cu
160
qJA 1.0 oz Cu
140
Power Curve 1.0 oz Cu
qJA, (°C/W)
120
1.3
1.2
100
1.1
80
qJA 2.0 oz Cu
60
1
0.9
40
20
0
1.4
TA = 25°C
0
100
200
300
400
500
600
COPPER HEAT SPREADER AREA (mm2)
0.8
0.7
700
Figure 4. SOT−223 qJA and PD vs. Cu Area
PC board design and the use of multilayer board material
will affect the thermal performance. See ON Semiconductor
application notes AND8220/D and AND8222/D for further
information.
Ambient operating temperature (TA) and estimated
device power will help determine which package to use.
Figures 2 and 4 can be used to quickly determine which
package and heat sink is a good candidate for the application.
incoming inspection of a CCR where the test times are a
minimum (t v 300 ms). DC steady−state (Ireg(SS)) testing is
applicable for application verification where the CCR will
be operational for seconds, minutes or hours.
ON Semiconductor has correlated the difference in Ireg(P) to
Ireg(SS) for stated board material, size, copper area and
copper thickness. Ireg(P) will always be greater than Ireg(SS)
due to the die temperature rising during Ireg(SS). This heating
effect can be minimized during circuit design with the
correct selection of board material, metal trace size and
weight for the operating current, voltage, and board
operating temperature (TA) and package. (Refer to the
Thermal Characteristics table in datasheet).
Current Regulation: Pulse Mode vs. Steady−State
NOTE: All curves are based upon a typical 30 mA CCR
device.
There are two methods of measuring current regulation:
Pulse mode (Ireg(P)) testing is applicable for factory and
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3
AND8391/D
The curves of Figure 5 for the SOD−123 and Figure 6 for
the SOT−223 packages show the relationship between Ireg
and time. Ireg decreases with time due to the effect of power
on the die.
Ireg vs. TIME
32
37
TA = 25°C
Vak = 7.5 V
36
TA = 25°C
Vak = 7.5 V
31.5
31
34
Ireg, (mA)
Ireg, (mA)
35
33
32
30.5
30
31
29.5
30
29
0
5
10
15
20
25
30
29
35
0
TIME (s)
5
10
15
20
25
30
35
TIME (s)
Figure 5. Typical SOD−123 30 mA, 300 mm2,
1 oz Cu, In Still Air
Figure 6. Typical SOT−223 30 mA, 300 mm2,
2 oz Cu, In Still Air
Correlation studies show that for each package steady
state Ireg there is a corresponding Pulsed Ireg value. Notice
on these two−terminal devices that the SOT−223 Ireg(P) has
a lower value than the SOD−123 Ireg(P), which results in
Ireg(SS) of 30 mA. This is due to the better RqJA of the
SOT−223. See Figures 7 and 8. The slope of the line in
Figures 7 and 8 will change if the actual footprint and board
thermal properties differ from the footprint listed in the
figures.
STEADY STATE CURRENT (Ireg(SS)) vs. Vak @ 30 mA
35
34
34
33
32
Ireg(SS), (mA)
Ireg(SS), (mA)
33
35
TA = 25°C
Vak = 7.5 V
31
30
29
TA = 25°C
Vak = 7.5 V
32
31
30
29
28
28
27
27
26
26
25
30 31 32 33 34 35 36 37 38 39 40 41 42 43
25
26
27
28
29
30
31
32
33
34
35
36
Ireg(P) (mA)
Ireg(P) (mA)
Figure 7. Ireg(SS) vs. Ireg(P) Testing SOD−123,
300 mm2, 1 oz Cu, In Still Air
Figure 8. Ireg(SS) vs. Ireg(P) Testing SOT−223,
300 mm2, 2 oz Cu, In Still Air
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37
AND8391/D
37
36
35 TA = −40°C
34
33
32
31
30
29
TA = 25°C
28
27
26
25
TA = 85°C
24
3 3.5 4 4.5 5
See ON Semiconductor application note AND8223/D for
additional information.
SOD−123 devices exhibit a greater negative temperature
coefficient as shown in Figure 9 than corresponding
SOT−223 devices as shown in Figure 10, due to the
difference in the package RqJA. The SOD−123 package
reaches thermal saturation with less power applied than the
SOT−223 package.
[−0.073 mA/°C
Typ @ Vak = 7.5 V
[−0.059 mA/°C
Typ @ Vak = 7.5 V
5.5 6 6.5 7
Vak (V)
7.5 8
8.5 9
36
35
34
33
32
31
30
29
28
27
26
25
24
23
22
21
20
Ireg(SS), (mA)
Ireg(SS), (mA)
The negative temperature coefficient trend of a SOD−123
CCR has a benefit as it avoids thermal runaway. There are
two areas of interest on the curves of Figure 9. The first is for
a given TA. Each curve shows a decrease in Ireg(SS) as Vak
increases and therefore PD increases. There also is the
ambient temperature affect on Ireg for a fixed Vak condition.
Both the SOD−123 (Figure 9) and SOT−223 (Figure 10)
show a decrease in Ireg(SS) as TA increases.
9.5 10
TA = 85°C
TA = 125°C
3
4.5 5
5.5 6 6.5 7
Vak (V)
7.5 8
8.5 9
9.5 10
Example 2:
Three Red LEDs with each having a VF of 2.0 Vdc @ 30
mA. Automotive battery voltage of 16 Vdc. Ambient
temperature max of 85°C. Available heat sink area for
device is 300 mm2 of 1 oz Cu.
PD of device = (16 Vdc – (3 x 2.0 Vdc) + 0.2 Vdc) x 30 mA
= 294 mW
SOD−123 PD max @ 85°C, 300 mm2 of 1 oz Cu = 182 mW
SOT−223 PD max @ 85°C, 300 mm2 of 1 oz Cu = 598 mW
The SOT−223 gives a margin of safety in the application.
Or, knowing that 294 mW of power needs to be dissipated,
we can select a SOT−223 device using 100 mm2 of 1 oz Cu.
For a series circuit (Figure 11), the power dissipation of
the CCR is determined by:
(Vsource – (VLEDS + VRPD)) x Ireg. Using the worst case
scenario; i.e, highest Vsource, Lowest LED VF, and highest
target Ireg. Using a 16 V source (auto voltage regulator high
output) driving two white LEDs with a Vf of 4.2 V, a reverse
protection diode (RPD) with a VF of 0.2 V and 30 mA Ireg
would give: (16 V − (2 x 4.2 V + 0.2 V)) x 0.030 A = 7.4 V
x 0.03 A = 222 mW.
For an ambient temperature of 85°C, from the PD curves
of Figures 1 and 3 a SOD−123 with 500 mm2 1 oz Cu would
1
3.5 4
suffice. A SOT−223 with 100 mm2 1 oz Cu would also
work.
Circuit Design
Example 1:
−DC
[−0.061 mA/°C
Typ @ Vak = 7.5 V
Figure 10. Typical SOT−223 30 mA, 300 mm2,
2 oz Cu, In Still Air
The following design examples will show how to
determine which package device and the Cu needed for a
simple circuit.
1
[−0.058 mA/°C
Typ @ Vak = 7.5 V
TA = 25°C
Figure 9. Typical SOD−123 30 mA, 300 mm2,
1 oz Cu, In Still Air
+DC
[−0.088 mA/°C
Typ @ Vak = 7.5 V
TA = −40°C
Reverse Battery Protection Diode (RPD)
D1
Anode
MBRS140T3
Q1
CCR
NSI45030T1G
Cathode
Automotive LED’s (3 mm2 − 4 Lead)
D3
D4
D2
1
2
1
2
2
LED
LED
Figure 11.
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LED
AND8391/D
Ireg(SS), (mA)
The following graphs show the relationship between
Ireg(SS) and TA for both the SOD−123 and SOT−223 for a
stated Cu area and thickness in still air. They also give the
slope of the line which can be used to estimate TJ at a specific
TA.
36
PD [ 260 mW
35
34
33
32 Est. T [ 54°C
J
31
Between −40°C & 25°C
30
−0.073 mA/°C
29
28
27
26
25
24
23
−40
−30
−20
−10
0
10
The formula for estimating TJ is: TJ = (PD x RqJA) + TA
(RqJA value from datasheet)
For the SOD−123 @ 25°C, TJ = (225 mW x 360°C/W) +
25°C = 106°C (as shown on the graph).
Ireg(SS) vs. TA
RqJA [ 360°C/W
Vak = 7.5 V
PD [ 225 mW
PD [ 198 mW
Est. TJ [ 106°C
Between 25°C & 85°C
−0.059 mA/°C
Est. TJ [ 156°C
20
30
40
50
60
70
80
TA (°C)
Ireg(SS), (mA)
Figure 12. Typical SOD−123 30 mA, 300 mm2, 1 oz Cu, In Still Air
36
PD [ 268 mW
35
34
33 Est. TJ [ −14°C
32
Between −40°C & 25°C
31
−0.088 mA/°C
30
29
28
27
26
25
24
23
−40
0
−30 −20
−10
RqJA [ 96°C/W
Vak = 7.5 V
PD [ 225 mW
Est. TJ [ 47°C
PD [ 192 mW
Between 25°C & 85°C
−0.072 mA/°C
Est. TJ [ 103°C
10
20
30
40
TA (°C)
60
70
80
Between 85°C & 125°C
−0.061 mA/°C
PD [ 174 mW
90
Est. TJ [ 142°C
100
110
Figure 13. Typical SOT−223 30 mA, 300 mm2, 2 oz Cu, In Still Air
PWM Current Control
CCR
Anode
The power dissipation of the CCR can be reduced when
used in a pulse width modulation (pwm) controlled circuit
Figure 14. The dc average current will be Ireg(SS) x duty
cycle %. For a typical 30 mA CCR at 20% duty cycle, TA of
25°C, the average current through the LEDs will be 6.0 mA.
Lead Input
CCR
Cathode
Control
Input
Output
Figure 14.
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120
130
AND8391/D
R(t) for 300 mm2 of 1 oz Cu for a SOD−123 from Figure 15
would be [ 90°C/W. Therefore; 216 mW x 90°C/W =
19.4°C temperature rise.
The device and heat sink will require analysis for worst
case condition to account for 100% duty cycle.
Figures 15 and 16 will assist to determine the temperature
rise caused by a power pulse.
Example: If the control input is a 500 Hz, 20% duty cycle
pwm applied to the three red LED circuit of Figure 11, the
1000
R(t) (°C/W)
50% Duty Cycle
100
20%
10
10%
5%
2%
1%
1
Single Pulse
0.1
0.000001
0.00001
0.0001
0.001
0.01
0.1
1
10
100
1000
100
1000
PULSE TIME (s)
Figure 15. SOD−123 NSI45030T1G PCB Cu Area 300 mm2 PCB Cu thk 1.0 oz
1000
5%
R(t) (°C/W)
100
50% Duty Cycle
20%
10%
10
2%
1
1%
Single Pulse
0.1
0.000001
0.00001
0.0001
0.001
0.01
0.1
1
10
PULSE TIME (s)
Figure 16. CCR SOT−223 NSI45030ZT1G PCB Cu Area 300 mm2 PCB Cu thk 2.0 oz
Summary:
The thermal behavior of a CCR is generalized in the
following matrix:
TA ↑
Heatsink Area ↑
Vak ↑
Ireg(SS)
↓
↑
NC*
TJ
↑
↓
↑
*In general SOD−123 for 3 V < Vak < 10 V, all other variables constant: Ireg(SS) changes < 2 mA (less @ TA > 25°C).
In general SOT−223 for 3 V < Vak < 10 V, all other variables constant: Ireg(SS) changes < 3 mA.
Figure 17.
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AND8391/D
APPENDIX A
SOD−123 devices are:
SOT−223 devices are:
NSI45020T1G, Steady State Ireg(SS) = 20 mA $15%
NSI45025T1G, Steady State Ireg(SS) = 25 mA $15%
NSI45030T1G, Steady State Ireg(SS) = 30 mA $15%
NSI45020AT1G, Steady State Ireg(SS) = 20 mA $10%
NSI45025AT1G, Steady State Ireg(SS) = 25 mA $10%
NSI45030AT1G, Steady State Ireg(SS) = 30 mA $10%
NSI45025ZT1G, Steady State Ireg(SS) = 25 mA $15%
NSI45030ZT1G, Steady State Ireg(SS) = 30 mA $15%
NSI45025AZT1G, Steady State Ireg(SS) = 25 mA $10%
NSI45030AZT1G, Steady State Ireg(SS) = 30 mA $10%
APPENDIX B
Application Note
Title
AND8349/D
Automotive Applications The Use of Discrete Constant Current Regulators (CCR) For CHMSL
Lighting
AND8220/D
How To Use Thermal Data Found in Data Sheets
AND8222/D
Predicting the Effect of Circuit Boards on Semiconductor Package Thermal Performance
AND8223/D
Predicting Thermal Runaway
The products described herein (NSI45020T1G, NSI45025T1G, NSI45030T1G, NSI45020AT1G, NS145025A51G, NSI45030AT1G, NSI45025ZT1G,
NSI45030ZT1G, NSI45025AZT1G, NSI45030AZT1G) have patents pending.
ON Semiconductor and
are registered trademarks of Semiconductor Components Industries, LLC (SCILLC). SCILLC reserves the right to make changes without further notice
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“Typical” parameters which may be provided in SCILLC data sheets and/or specifications can and do vary in different applications and actual performance may vary over time. All
operating parameters, including “Typicals” must be validated for each customer application by customer’s technical experts. SCILLC does not convey any license under its patent rights
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